Zn stimulates the production BMP4 by ECs. (A) 6- to 8-week-old female C57BL/6 mice were fed a normal or ZD diet for 21 days, at which point mice were given 550 cGy TBI. One cohort was given supplemental Zn in drinking water (300 mg/kg per day of ZnSO₄) from day 0. Levels of BMP4 were quantified by ELISA at day 10 after TBI (n = 5-10/group from 1 independent experiment). (B-C) Six- to 8-week-old female C57BL/6 mice were given supplemental Zn in drinking water (300 mg/kg per day of ZnSO₄) for 21 days, at which point mice were given 550 cGy TBI. Mice were maintained on Zn-supplemented drinking water for the duration of the study. (B) BMP4 levels measured by ELISA at day 10 (n = 9/group combined from 3 independent experiments). (C) ECs were FACS purified at day 7 and Bmp4 expression was measured by qPCR (n = 6/group combined from 2 independent experiments). (D-E) exECs were generated as previously described^26,32 and stimulated for 24 hours with ZnSO₄ at the indicated concentrations and Bmp4 expression measured by qPCR at 24 hours (50 μM: n = 8/group combined from 3 independent experiments; 100 μM: n = 11/group across 5 independent experiments) (D), and BMP4 protein was quantified by ELISA at 48 hours (n = 3 independent experiments) (E). (F) Six- to 8-week-old female C57BL/6 mice were given supplemental Zn in drinking water (300 mg/kg per day of ZnSO₄) for 21 days, at which point mice were given 550 cGy TBI. Mice were administered with the BMP type I receptor inhibitor dorsomorphin dihydrochloride (12.5 mg/kg) intraperitoneally at day −1 before TBI and twice daily after TBI, and all mice were maintained on ZnSO₄ in drinking water for the duration of the study. Total thymus cellularity was quantified at day 10 after TBI (n = 5/group from 1 independent experiment). Graphs represent mean ± SEM; each dot represents a biologically independent observation. *P < .05; **P < .01; ***P < .001.